A hacker group is claiming responsibility for exploiting a zero-day flaw in the vBulletin Internet forum . Hackers are bragging that they broke into both the MacRumors.com and vBulletin.com forums.

VBulletin Solutions, the company that develops the online forum software, reset all account-holder passwords on Friday. The company has confirmed that customer log-in credentials were indeed stolen.

“Very recently, our team discovered sophisticated attacks on our network, involving the illegal access of forum user information, possibly including your password,” the company said on its bulletin board. “Our investigation currently indicates that the attackers accessed customer IDs and encrypted passwords on our systems. We have taken the precaution of resetting your account password. We apologize for any inconvenience this has caused but felt that it was necessary to help protect you and your account.”

A $7,000 Exploit?!

The Inj3ct0r Team, the hacker group that claims to be behind the attack, posted a note on Facebook saying that it not only hacked vBulletin.com and Macrumors.com but also got to the shell, the database and the root server. The hackers wanted to prove that “nothing is this world” is safe.

“We found a critical vulnerability in vBulletin all versions 4.x.x and 5.õ.x. We've got upload shell in vBulletin server, download database and got root,” the hackers wrote. “Macrumors.com was based on vBulletin CMS. We use 0day exploit on vBulletin, got password moderator. 860000 hacked too. The network security is a myth.”

The Inj3ct0r Team offered to sell the vulnerability for $7,000. The post generated more than 190 likes, 49 shares, and 58 comments as of the time of this writing. One Facebooker named Kori Stroud said, “No one will pay $7000 for this or any other exploit. But good try though.”

Is It a Scam?

Brian Krebs, a former Washington Post reporter who now runs KrebsonSecurity, reports that several individuals do indeed appear to be selling what they claim are zero-day exploits in vBulletin 4.x and 5.x, including the attackers who first contacted him on Thursday claiming responsibility for the break-in.

“That person, using the nickname Inj3ct0r, advertised a copy of the supposed exploit for $7,000, available for payment via virtual currencies Bitcoin and WebMoney,” he wrote in a blog post. “According to this user’s Bitcoin wallet, at least one person appears to have paid for a copy, sending the user 15 Bitcoins on Nov. 15 (when Bitcoin’s value was approximately $435 per BTC, according to Bitcoincharts.com).”

As Krebs sees it, the person who posted on Friday may have seen an opportunity to generate or scam interested buyers by offering to sell the same exploit for just $200 in Bitcoins. Although Krebs said it’s unclear if that sale was for real or a scam, several buyers apparently thought it worthwhile and cheap enough to verify the claim with a payment.